Updated June 08, 2015.

We expect to see people’s life expectancy vary based on whether or not they smoke, how much they exercise, how much they weigh and their family history of certain illnesses (see these life expectancy calculators to figure out your own life expectancy). What we do not expect to be a factor in how long we live is our birth year. That’s right, the year you were born in can impact your life expectancy by as much as 1.5 years.

Why? Because of the sun (and not because of skin cancer). If that sounds weird, just hold on to your hat as we explore the impact of the sun on your life expectancy.

The Sun and Average Life Expectancy

As you know, the sun puts out ultraviolet radiation. This radiation hits our skin and causes a wide variety of things to happen in our bodies (such as tanning, sunburns and the produce of vitamin D). One thing it also seems to do is directly impact life expectancy. Basically, in a study of over 300,000 people born in Maine, the people who were born in a peak solar year lived 1.5 years less than those born in nonpeak years.

Peak Solar Year – What Is That?

The sun doesn’t just put out the same amount of energy each year – it has a cycle. It ebbs and flows. In peak solar years, there is more solar activity, more solar flares and (consequently) more ultraviolet radiation. These cycles run about 11 years and then repeat. What researchers did was compare the life expectancies for people born in the three years with the most solar activity to those born in other years.

They found, after controlling for other factors, that people born in these peak solar years lived an average of 1.5 years less.

Why Does Peak Solar Year Matter?

That’s pretty much a guessing game at this point. One course of thinking is that high levels of ultraviolet radiation suppress the immune system of pregnant women, and these changes impact how fetus’ express genes (in other words, when there is a suppressed maternal immune system, certain genetic switches get turned “on” or “off” that impact health negatively later in life). Interestingly, men seemed more affected by the solar flare effect then women.

Hmmm.

Yeah, that’s what I say. This is a weird link between solar activity and life expectancy. The authors of the study talk a lot about the evolutionary impact of the finding (that changes in the environment can make changes in genetic expression), but that doesn’t seem the interesting part. What I want to know is, what should we do about it? Should pregnant women in peak solar years stay indoors more? Does this only matter for people in Maine, who are exposed to solar radiation differently than people in other places because of skin color and latitude? There are a lot of unanswered questions here. Furthermore, there doesn’t seem to be a lot of interest in answering them. I haven’t seen studies adjusting life expectancy predictions by birth year based on peak solar activity (though if they ran the variable, then it may explain away some of the variation in life expectancy and increase the significance of their findings). Meanwhile, consider this an interesting side fact and don’t lose any sleep over it. There could be other explanations, and besides, if the authors of the study are right, you can’t do anything about it anyway.
<sub>Source(s):

Lowell WE, Davis GE Jr. The light of life: evidence that the sun modulate human lifespan. Med Hypotheses. 2008; 70(3):501-7. 2007 Oct 22.</sub>